1. Field of the Invention
The present invention relates to a method and apparatus for improving coupling between a surface wave plasma (SWP) source and plasma and, more particularly, to a method and apparatus for improving the coupling between the SWP source and plasma using a mode scrambler.
2. Description of Related Art
Typically, during semiconductor processing, a (dry) plasma etch process is utilized to remove or etch material along fine lines or within vias or contacts patterned on a semiconductor substrate. The plasma etch process generally involves positioning a semiconductor substrate with an overlying patterned, protective layer, for example a photoresist layer, into a processing chamber. Once the substrate is positioned within the chamber, an ionizable, dissociative gas mixture is introduced within the chamber at a pre-specified flow rate, while a vacuum pump is throttled to achieve an ambient process pressure. Thereafter, a plasma is formed when a portion of the gas species present are ionized following a collision with an energetic electron. Moreover, the heated electrons serve to dissociate some species of the mixture gas species and create reactant specie(s) suitable for the exposed surface etch chemistry. Once the plasma is formed, any exposed surfaces of the substrate are etched by the plasma. The process is adjusted to achieve optimal conditions, including an appropriate concentration of desirable reactant and ion populations to etch various features (e.g., trenches, vias, contacts, etc.) in the exposed regions of substrate. Such substrate materials where etching is required include silicon dioxide (SiO2), poly-silicon and silicon nitride, for example.
Conventionally, various techniques have been implemented for exciting a gas into plasma for the treatment of a substrate during semiconductor device fabrication, as described above. In particular, (“parallel plate”) capacitively coupled plasma (CCP) processing systems, or inductively coupled plasma (ICP) processing systems have been utilized commonly for plasma excitation. Among other types of plasma sources, there are microwave plasma sources (including those utilizing electron-cyclotron resonance (ECR)), surface wave plasma (SWP) sources, and helicon plasma sources. These conventional systems typically provide a single vacuum chamber space wherein the ionizable gas for creating the plasma is mixed with the dissociative gas used for processing. The present inventors have recognized, however, that these conventional plasma processing systems suffer from a number of deficiencies.
First, providing ionization and dissociative gas in a common chamber provides limited control of process chemistry (i.e., control of chemistry dissociation). Moreover, a common plasma and processing space exposes the plasma source to process gasses that may erode or deposit material on the plasma source thereby affecting the operation of the plasma source. Similarly, a common gas mixture space may cause substrate damage due to interaction of the substrate with energetic electrons and ions of the plasma. Still further, the inventor has recognized that the conventional systems are limited to conventional techniques for controlling substrate processing uniformity, such as controlling the temperature of the substrate to compensate for non-uniformity of the plasma and/or process gasses.